The invention relates to a device for changing the control timing of gas exchange-valves of an internal combustion engine, and it is particularly advantageous for application in hydraulic camshaft adjusting devices of the rotary piston type.
A device of this type is already known from European patent EP 0 816 610A2, which generally defines this class. This device, designed as a so-called vane-cell positioner, is formed essentially of a drive gear directly connected to a crankshaft of the internal combustion engine and an impeller that is directly connected to a camshaft of the internal combustion engine. The drive gear has a cavity formed by a hollow cylindrical perimeter wall and two sidewalls, inside of which five hydraulic working chambers are formed from five boundary walls. Accordingly, the impeller has at the perimeter of its wheel hub five vanes, each of which extends radially into a working chamber of the drive gear. These five vanes divide each of the working chambers into two counteracting hydraulic pressure chambers. The outer end of each vane of the impeller is radially pressed against the inside of the perimeter wall of the drive gear from the force of a spring element located in an axial retaining notch at the inner end of the vane. This seals off the pressure chambers of each hydraulic working chamber from one another and effects, by selectively or simultaneously applying pressure using a hydraulic pressure medium, a pivoting motion or a fixing of the impeller with respect to the drive gear and thus the camshaft with respect to the crankshaft.
The disadvantage in this known device is that when pressure is applied to one or both pressure chamber(s) of each hydraulic working chamber, a buildup of pressure results in the sealing gap between the outer end of each vane and the inside of the perimeter wall of the drive gear. If the force of the pressure exceeds the value of the spring force of the spring element located at the inner end of each vane, a so-called xe2x80x9cvane dippingxe2x80x9d can occur despite these spring elements, i.e. the vane can radially shift against the force of the spring element. This then results in increased pressure medium leakage between the individual pressure chambers of the hydraulic working chamber so that a poorer hydraulic lock of the impeller with respect to the drive gear results. Moreover, this increased pressure medium leakage is the cause of larger deviations in the prescribed positioning angle between the camshaft and the crankshaft as well as of slower positioning times of the device.
The object of this invention is to provide a device for changing the control timing of gas exchange valves of an internal combustion engine, in particular a hydraulic camshaft adjustment device of the rotary piston type, whereby the radial shift of the vanes against the force of their spring elements resulting from the pressure buildup in the sealing gap between the outer end of each vane of the impeller and the inside of the perimeter wall of the drive gear is effectively eliminated.
According to the invention, this object is met by a device having a drive gear adapted to be directly connected to a crankshaft of the internal combustion engine and an impeller adapted to be directly connected to a camshaft of the internal combustion engine, with the drive gear having a cavity formed by a hollow cylindrical perimeter wall and two side walls inside of which at least one hydraulic working chamber is formed from at least two boundary walls. The impeller has a wheel hub with at least one vane at the perimeter thereof extending radially into a working chamber of the drive gear that divides the chamber into two respective hydraulic pressure chambers that counteract one another. An outer end of each vane of the impeller is radially pressed against the perimeter wall of the drive gear as a result of force of a spring element located in an axial retailing notch at an inner end of the vane. The pressure chambers are adapted to effect a pivoting motion or a fixing of the impeller with respect to the drive gear, and thus of the camshaft with respect to the crankshaft, by selective or simultaneous application of pressure with a hydraulic medium. The spring elements at the inner end of the vanes have a spring force, at constant space requirements, that is higher than the maximum pressure force by the hydraulic pressure medium acting on the outer end of the vanes in the respective actuated pressure chamber of the device.
The maximum pressure force of the hydraulic pressure medium is equal to the pressure peaks that arise according to operation and act on one or the other axial side of the outer ends of the vanes according to which pressure chamber of the device is actuated. Also, when both pressure chambers are simultaneously actuated, these pressure peaks act on the entire surface area of the outer ends of the vanes. However, since the spring force of the spring elements is aided by the centrifugal forces acting on the vanes when the engine is running as well as by the pressure force of the hydraulic pressure medium that also acts on half or all of the surface of the inner ends of the vanes, it has proven to be sufficient in preventing the disadvantageous vane dipping if the spring elements have a minimum spring force that is approximately equal to the maximum pressure force of the hydraulic pressure medium. The implementation of this minimum spring force by appropriately dimensioning the spring elements is, however, subject to certain limits due to the generally very limited space in the retaining notches of the spring elements.
One way to nevertheless increase the spring force of the spring elements to the required minimum spring force is the special geometric structuring of the spring elements along their axial length. In a first preferred embodiment, the spring elements are therefore provided as radially wave-shaped bent spring packets made of at least two flat profile springs that each have a concave center and two convex ends along their axial length. However, up to a limit determined by space requirements, it is also possible to arrange more than two of these types of flat profile springs on top of one another that are connected together an adhesive or the like to make installation easier. The concave center of these spring packets lies preferably on the base of the notch of the axial retaining notches of the vanes, whereas their convex ends lie against the axial edges of the inner ends of the vanes. It is, however, also possible to place the spring packets in reverse into the retaining notches of the vanes so that each of the spring packets"" center lies against the inner end of the vane and the ends of the spring packets lie on the base of the notch of the retaining notch of the vane.
A second preferred embodiment of geometrically spring-force enhanced spring elements is the suggestion of providing the spring elements as radial wave-shaped bent round profile springs with at least two spring sides running parallel with one another, each of which also has a concave center and two convex ends along its axial length. The number of spring sides running next to one another, however, is also subject to limits of space requirements in this embodiment as well, for which the concave center of the round profile springs is also preferred to lie on the base of the notch of the axial retaining notches and their convex ends are preferred to lie against the inner ends of the vanes.
A third embodiment whose goal is to equip spring elements of the vanes with the required minimum spring force using special geometric shapes provides the spring elements as radial Z-shaped bent riser, upright springs. These upright springs each include an axially straight, eyelet-shaped base and a head that is parallel to it and similarly shaped, which are connected together through a slanted spring stem. The base of these upright springs lies flat on the base of the notch of the axial retaining notches, whereas its head lies flat against the inner ends of the vanes. The special advantage of these types of springs is that they apply a relatively large contact force on the vanes and at the same time can smooth out larger tolerance differences.
A fourth preferred embodiment of geometrically spring-force enhanced spring elements is suggested in which they are provided as radial convex bent hairpin springs whose spring sides are positioned parallel one on top of the other and lying against one another and are connected together through a hairpin eyelet. One end of this hairpin spring formed by the hairpin eyelet and its opposite other end are placed in the axial retaining notches on the base of the notch of the axial retaining notches, whereas its center lies against the center of the inner end of the vane. It would also be conceivable, however, to have a reverse arrangement of springs in the axial retaining notches of the vanes.
A fifth preferred embodiment of geometrically spring-force enhanced spring elements is suggested in which the spring elements are provided as loose coil springs that have approximately twice the axial length as the axial retaining notches of the vanes and are placed into the retaining notches of the vanes as a continuous loop that is radially compacted. Here, the high radial spring force of the individual spring windings of coil springs is used mainly to be able to apply a large contact force onto the vanes.
Finally, a sixth preferred embodiment of geometrically spring-force enhanced spring elements is suggested in which the spring elements are provided as spring cushions made of an elastic temperature resistant material. These spring cushions correspond in length and width approximately with the dimensions of the axial retaining notches of the vanes and have a height that is a bit larger than the distance between the base of the notch of the axial retaining notches and the inner ends of the vanes lying against the perimeter wall of the drive gear. The higher the spring cushions are designed, the higher the contact force that is applied to the vanes. As material for the spring cushions, rubber or elastomers have proven to be especially advantageous, but foam plastics or the like can also be used.
The device according to the invention for changing the control timing of gas exchange valves of an internal combustion engine, in particular a hydraulic camshaft adjustment device of the rotary piston type, has the advantage in comparison to known devices from the state of the art in that spring elements located at the inner end of the vanes exhibit, in all embodiments described, a sufficient minimum spring force to prevent the radial shift of the vanes resulting from the pressure buildup in the sealing gap between the outer end of each vane of the impeller and the inside of the perimeter wall of the drive gear. This reduces the internal pressure medium leakage between the individual pressure chambers of the hydraulic working chambers to a minimum and improves the hydraulic locking of the impeller with respect to the drive gear as well as the maintaining of prescribed positioning angles between the camshaft and the crankshaft.
Moreover, the enhanced spring elements according to the invention are not just suitable for pressing the vanes of the impeller against the perimeter wall of the drive gear of a vane-cell positioning device, but are also applicable as spring element sealing strips to an impeller of a so-called pivoting vane positioning device.